It would depend what it meant. If it meant resitting GCSE until you pass, then yes, I’d be ok with that, as level 2 is very basic; but insisting everyone takes A level maths seems more than a little pointless. Also, would there be similar requirements to study English? I would apply the same thinking to that, if so. Everyone should be at least at level 2 before leaving school, but there is a big gap to get to A level. There has to be more nuance than that I think.
Having said that, I don’t have an O level in maths, and I have 3 degrees, two of which are postgraduate, one of those requiring the use of statistics in the dissertation. It’s by no means essential.